This section is intended to provide a background to the various embodiments of the technology described in this disclosure. The description in this section may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and/or claims of this disclosure and is not admitted to be prior art by the mere inclusion in this section.
In Long-Term Evolution (LTE), a UE has two Radio Resource Control (RRC) states, i.e., a RRC_Idle state and a RRC_Connected state, and has two types of downlink control channels, i.e., Physical Downlink Control Channel (PDCCH) and Enhanced Physical Downlink Control Channel (E-PDCCH), to schedule a data channel, i.e., to indicate data required by the UE on the data channel.
In the RRC_Idle state, information to be received by the UE may include non-UE-dedicated information, such as system information, paging, and Message 2 (MSG2) in a random access procedure etc. In the RRC_Connected state, information to be received by UE may include not only UE-dedicated information, but also the non-UE-dedicated information.
Decoding of the PDCCH by the UE is based on a cell reference signal (CRS) and therefore the PDCCH cannot be beamformed to the UE. Due to this shortcoming, the E-PDCCH is introduced. The E-PDCCH can be beamformed to the UE as decoding of the E-PDCCH is based on a demodulation reference signal (DMRS) which is UE specific.
When UEs are in their RRC_Idle state, the downlink control channel used to schedule the data channel can only be PDCCH, as the network node won't need to tell one from another among those UEs and corresponding E-PDCCHs are not configured for now. Therefore, the E-PDCCH cannot be used in UE's RRC_Idle state.
In the RRC_Connected state, the downlink control channel used to schedule the downlink data channel depends on whether the UE is configured with E-PDCCH or not. If the E-PDCCH is not configured, the PDCCH is still used to schedule the data channel. If the E-PDCCH is configured, both the PDCCH and the E-PDCCH are used to schedule the data channel. That is, in the RRC_Connected state, the UE still needs to monitor the PDCCH, even if the E-PDCCH is configured. This is due to two reasons. First, there is no common search space in the E-PDCCH, so when the UE in the RRC_Connected state needs to receive system information, paging etc., the UE still needs to monitor the PDCCH. Second, the E-PDCCH may collide with Master Information Block (MIB) or Primary Synchronization Signal (PSS)/Secondary Synchronization Signal (SSS) in some subframes, therefore in those subframes, the PDCCH is still needed to receive the UE-dedicated information. To summarize, although the E-PDCCH is an enhancement compared to the PDCCH, it cannot replace the PDCCH in the RRC_Connected state of the UE. The UE needs to monitor both the PDCCH and the E-PDCCH channels in the RRC_Connected state.
In a next generation of wireless communication network, a UE has three RRC states, i.e., a RRC_Idle state, a RRC_Active state and a RRC-Dormant state.
The RRC_Active state is similar to the RRC_Connected state in LTE, where there is UE context in a Radio Access Network (RAN) and mobility of the UE is network controlled. The RRC_Idle state is similar to the RRC_Idle state in LTE, where there is no UE context in the RAN and mobility of the UE is UE controlled. The RRC_Dormant state is a new state in the next generation of wireless communication network, where there is UE context in the RAN but mobility of the UE is UE controlled. In the RRC_Dormant state, the UE needs to receive paging, system information from RAN as the network does not know where the UE is.
The next generation of wireless communication network is based on an ultra-lean design whose intention is that as little mandatory transmissions as possible will be regulated. This implies that there will likely not be any CRS signals in the next generation of wireless communication network and hence no CRS-based PDCCH as LTE uses. Instead, downlink control channels in the next generation of wireless communication network need to be UE-configured and consist of definitions of a reference signal, a synchronization signal and a search space for reception of downlink control information.
Similar to LTE, a broadcast downlink control channel, e.g., a broadcast PDCCH (also referred to as a non-UE-dedicated PDCCH), is needed to receive broadcast information (also referred to as non-UE-dedicated information, e.g. system information, paging etc.) and a UE-dedicated downlink control channel, e.g., a UE-dedicated PDCCH, is needed to receive UE-dedicated information (also referred to as UE-dedicated information).
In the RRC_Active state, the UE still needs to receive UE-dedicated information via the dedicated PDCCH channel and to receive non-UE-dedicated information via the broadcast PDCCH channel. And in the RRC_Dormant state, some design mentioned that the UE may receive the UE-dedicated information via the dedicated PDCCH channel and the non-UE-dedicated information via the broadcast PDCCH channel as well.
However, if the design in the next generation of wireless communication network is similar with LTE, i.e. the UE is required to monitor more than one downlink control channel in some state, such as the RRC_Active state, or the RRC_Dormant state, it requires the UE to perform a substantial amount of processing, which consumes battery power.
Therefore, power consuming of the UE caused by the hypothesis mentioned above would be a concern for the next generation of wireless communication since battery power is a bottleneck of UE performance.